As much as 40% of the population over 65 years of age suffers from sleep disturbance, a condition which frequently leads to problematic use of hypnotic medications, reduced quality of life, and increased morbidity and mortality. Available data, from both human and animal studies, strongly suggest that certain non- pharmacological treatments may provide a safer, potentially more effective alternative in the management of sleep disturbance in elderly. The primary features of sleep disturbance in the elderly, fragmented nocturnal sleep, early morning awakenings and increased daytime sleepiness, appear to reflect changes in the circadian timing system, both in terms of reduced amplitudes and altered phase relationships. Studies have shown that timed exposure to bright light may be effective in shifting the phase of circadian rhythms, as well as increasing the amplitudes of the rhythms. However, no studies have directly addressed the effects of timed exposure to bright light on sleep disturbance in the elderly, under conditions of normal daily life. This proposed two-phase project will intensively study light exposure in relation to sleep disturbance in 40 elderly subjects. In Phase 1, baseline levels of light exposure will be correlated with physical activity and with subjective assessments and objective measures of sleep disturbance. In Phase 2, we will evaluate the short-term effects of timed bright light exposure on the disturbed sleep patterns of these subjects. The research proposed here will be the first to record chronobiological variables in sleep disturbed elderly subjects in a natural setting, thus providing valuable etiologic data on this group. These studies will also be the first to test the efficacy of a promising, non-pharmacological treatment for sleep disturbance, under conditions of normal daily living. It is expected that this important first study will form the basis for subsequent investigations to evaluate: (a) the long term effectiveness of bright light therapy in controlling sleep disturbance and enhancing quality of life and health in the elderly, and (b) the application of these approaches to other clinical conditions (e.g. Alzheimer's disease, autism/retardation), and settings, (e.g. nursing homes).